"V. M." <txian@hotmail.com> writes:
> sometimes i'm getting:
> NOTICE: Child itemid in update-chain marked as unused - can't
> continue repair_frag
> during a simple "vacuum", db is online.
> pg version 7.1, on debian linux kernel 2.4.
> what's the problem?
The source code says:
/* * This means that in the middle of chain there * was tuple updated by older (than
XmaxRecent) * xaction and this tuple is already deleted by * me. Actually, upper part of chain
shouldbe * removed and seems that this should be handled * in scan_heap(), but it's not
implementedat the * moment and so we just stop shrinking here. */
In short, an unimplemented special case in VACUUM's logic that tries to
compact out free space by moving tuples around.
Most people never see this message though. There must be something
unusual about the pattern of updates being done on this particular
table, that you see it often.
regards, tom lane